1. Field of the Invention
The present invention relates to a liquid crystal display device and to a driving control circuit and driving method to be used in the liquid crystal display, and more particularly to the liquid crystal display device suitably used for displaying moving images and to the driving control circuit and driving method to be used in the liquid crystal display device.
The present application claims priorities of Japanese Patent Application Nos. 2006-101252 filed on Mar. 31, 2006 and 2006-159001 filed on Jun. 7, 2006, which are hereby incorporated by reference.
2. Description of the Related Art
In recent years, a liquid crystal display device is used not only as a monitor of personal computers but also as a display for television sets or a like. In its application to television sets, performance of displaying moving images is required. However, in conventional liquid crystal displays, when moving images are displayed, while a current image remains persistent in a user's consciousness, a subsequent image is displayed, which causes an afterimage (trail-leaving and/or blurring of moving images) to be seen by users. The reason for this is that much time is required for a response to a voltage applied to the liquid crystal and holding-type driving is performed in which a current frame is held until a display signal corresponding to a succeeding frame is supplied.
A trail-leaving phenomenon caused by the response speed of a liquid crystal can be reduced by increasing the response speed of the liquid crystal by performing an overdriving operation in which an over voltage is applied to the liquid crystal. Also, a trail-leaving phenomenon caused by holding-type driving can be reduced by using an impulse driving method in which an image is displayed only for a moment as in the case of a CRT (Cathode Ray Tube) display device. The impulse driving method includes, for example, a black insertion driving method in which a black image is displayed after displaying of an image on a liquid crystal display panel during one frame period. The impulse driving method also includes another method (backlight blinking method) in which a backlight is turned on after the application of a specified voltage to an image region.
The conventional liquid crystal display device of the type, described above and shown in FIG. 18, includes a black insertion driving control section 1, a source driver 2, a gate driver 3, and a liquid crystal display panel 4. The liquid crystal display panel 4 has a plurality of rows of scanning electrodes (not shown), a plurality of columns of data electrodes (not shown) and a plurality of pixel regions, in which a scanning signal “OUT” is successively applied to each of the scanning electrodes and corresponding display data D is fed to each of the data electrodes and the corresponding display data D is written into each of pixel regions and control is exerted on light from a backlight (not shown) in a manner to correspond to each display data D. The black insertion driving control section 1 sends out, in response to an input video signal VD, a control signal “a” to the source driver 2 and a control signal “b” to the gate driver 3. The source driver 2 applies, in response to the control signal “a” fed from the black insertion driving control section 1, a voltage (display data voltage) corresponding to display data based on the input video signal VD to each of the data electrodes of the liquid crystal display panel 4 and then the black insertion driving operation is performed in which a black frame having a gray level of, for example, “0” is uniformly inserted during each frame period. The gate driver 3, in response to the control signal “b” fed from the black insertion driving control section 1, applies line-sequentially a scanning signal OUT to each of the scanning electrodes of the liquid crystal display panel 4.
In the conventional liquid crystal display device, as shown in FIG. 19, each of scanning electrodes (corresponding to lines 1, 2, . . . , 2N−1, 2N) of the liquid crystal display panel 4 is line-sequentially driven and, after display data [1] corresponding to the input video signal VD is written into a corresponding pixel region, black data is written and one frame ends. Thereafter, the similar operations by the application of display data [2], [3], [4], and black data are repeated for every frame. As a result, as shown in FIG. 20, a driving frequency for a liquid crystal display panel 4 becomes twice as high as a frame frequency and a frequency of a signal for each of the display data D, control signal “a”, control signal “b” and scanning signal OUT doubles when compared with the case of no black insertion driving and time required for writing into the liquid crystal display panel and time for holding the written pixel data are reduced to half when compared with the case of no black insertion driving. Furthermore, a frequency of the inversion of the polarity of display data voltage D doubles and, therefore, a frequency of the control signal “a” shown in FIG. 18 doubles as well.
In addition to the liquid crystal display device described above, other liquid crystal display devices of this type are disclosed, for example, in following reference. In the driving method of a conventional liquid crystal display device for a TV (Television Set) disclosed in Japanese Patent Application Laid-open No. Hei 04-044478, as shown in FIG. 21, an interlaced driving operation is performed in each odd field during which each of odd-numbered rows of scanning electrodes out of scanning electrodes (corresponding to lines 1, 2, . . . , 2N−1, 2N) of the liquid crystal display panel is successively driven and in each even field during which each of even-numbered rows of scanning electrodes is successively driven. The odd field and even field appear repeatedly with time width of a refresh rate. In the former half of the odd-field, display data ([1], [3], . . . ,) corresponding to an input video signal is written in each pixel region corresponding to the odd-numbered rows of scanning electrodes, while, in the latter half of the odd-field, black data is simultaneously written in each of pixel regions corresponding to all odd-numbered rows of scanning electrodes. Moreover, in the former half of the even field, display data ([2], [4], . . . ,) corresponding to an input video signal is written in each of pixel regions corresponding to the even-numbered rows of scanning electrodes and, in the latter half of the even field, black data is simultaneously written in each of the pixel regions corresponding to all even-numbered rows of scanning electrodes.
However, the conventional liquid crystal display device described above has following problems. That is, the liquid crystal display device shown in FIG. 18 presents a problem in that, an operational frequency for each component doubles when compared with the case of no black insertion driving and, therefore, hardware configurations corresponding to the doubled driving frequency are required, as a result, causing an increase in scale and in power consumption. Also, the conventional liquid crystal display device presents another problem in that each of the scanning electrodes is line-sequentially driven and, as shown in FIG. 20, the polarity of a voltage of display data D is inverted on every line and this inverted pattern is reversed again per every refresh rate and, therefore, the polarity of the voltage of display data is biased in some regions on the liquid crystal display panel, causing the occurrence of a screen burn-in. In addition, though the problem of trail-leaving is improved by black insertion driving, alternate flashing occurs between the time for black display and time for video display in a frequency band in which a human can recognize, which causes an increase of flickering on a screen. In order to suppress the flickering, a refresh rate needs to be raised to a degree to which a human cannot recognize, which, as a result, the operational frequency doubled by the black insertion driving is further increased twice, thus causing a difficulty in hardware configurations.
Moreover, the driving method disclosed in Japanese Patent Application Laid-open No. Hei 04-044478 presents a problem in that, though an operational frequency of a signal for each component is allowed to be made lower by performing the interlaced driving operation, since, in the latter half of an odd field, black data is simultaneously written in each of pixel regions corresponding to all the odd-numbered rows of scanning electrodes and, in the latter half of the even field, black data is simultaneously written in each of the pixel regions corresponding to all the even-numbered rows of scanning electrodes, time for holding the written black data varies on every line, which causes a variation in luminance between an upper part and lower part of a display screen.